1. Field of the Invention
This invention lies in the field of methods for the production of esters from phenolic compounds and carboxylic acids.
2. Description of the Prior Art
Various catalysts and catalyst systems have heretofore been taught for the esterification of compounds having phenolic hydroxyl groups with organic carboxylic acids.
For examples, Kong-Chan U.S. Pat. No. 4,478,754 teaches the uses of boric anhydride as the catalyst to make sulfonated carboxylic acid esters of phenol; Lowrence U.S. Pat. No. 3,772,389 uses a catalyst system of boron compound and sulfonic acid; and Knickmeyer et al U.S. Pat. No. 4,271,311 discloses a catalyst system of boron compound and certain alkali metal salts.
The use of aliphatic and aromatic esters of phosphorous acid as catalysts is taught in Harrison U.S. Pat. No. 2,622,071. No mention or suggestion of using inorganic phosphorous acids as catalysts is made.
All of such prior art catalysts and catalyst systems, and the phenolic esterification processes employing such, result so far as now known in the production of ester products which are in an impure state with such product being characteristically significantly colored and being in admixture with undesired by-products, the latter being produced, it appears, mainly by Fries rearrangement. Before these prior art ester products can be used, for example, as starting materials for sulfonation to produce sulfonated carboxylic acid esters of phenol, they must be purified and decolored in order to result in a final product of commercially acceptable quality.
There is a need in the art for a new and improved catalyst which permits production of high purity, low color ester from starting materials comprising phenolic compounds and carboxylic acids.